Method of making a glass body with a phosphorous- and porous SiO2-containing coating, glass body made thereby and solution for making same

ABSTRACT

The glass body used in a solar energy apparatus is provided with an adherent and anti-reflective coating on at least one of its sides. The coating contains phosphorous and porous SiO 2  and preferably has a rubbing resistance criterion according to DIN 58196-5, intensity of testing H50, of 2 or better. The method of providing the glass body with the coating includes dipping the glass body in a H 3 PO 4 - and SiO 2 -containing volatile solution, withdrawing the glass body at a speed of from 1 mm/s to 20 mm/s from the solution and tempering the glass body at a temperature of under T g  of the glass. The solution for making the coating containing porous silica and phosphorous is also part of the invention. It preferably has a pH of from 1 to 2 and contains from 0.1 to 2 percent by weight of HNO 3  or HCl, a lower alcohol with from one to five carbon atoms, from 0.1 to 3.5 percent by weight H 3 PO 4  and from 0.5 to 7 percent by weight of an SiO 2  sol.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a glass body with a porous coating and method for making it as well as a solution for making the porous coating.

[0003] 2. Description of the Related Art

[0004] EP 0 897 898 A2 describes a method for depositing an optical coating on a flat glass plate composed of soda lime glass by means of a sol or sol mixture.

[0005] In U.S. Pat. No. A 2,601,123 a method of making a porous SiO₂ coating on glass is described. This sol gel coating method based on the use of a sol with a highly dispersed SiO₂ particles comprises a simple dipping step that provides a porous SiO₂ coating on soda lime glass.

[0006] DE 199 18 811 A1 discloses a process, in which a standard pre-stressed safety glass, also a soda lime glass, is provided with a porous SiO₂ coating.

[0007] Also DE 196 42 419 A1 and DE 100 18 697 A1 describe methods for making porous coatings.

[0008] A typical composition of soda lime glass, in percent by weight on an oxide basis, is 72%, SiO₂; 14%, Na₂O (+K₂O); 9%, CaO; 3to 4%, MgO; and 1%, Al₂O₃.

[0009] DE 1 941 191 describes a process for making transparent, glassy, crystalline or glassy-crystalline inorganic multi-component materials, preferably in thin layers. Above all, sensitive glasses that can be attacked, for example, by water should be protected with these layers.

[0010] K. Cathro, D. Constable u. T. Solaga, state that porous SiO₂ coatings adhere only poorly to borosilicate glass in Solar Energy 32 [5], p. 573 (1984). A modification of this method which is especially applicable to PYREX® is suggested, in which an after-treatment step in which the glass is immersed in a sodium bicarbonate (NaHCO₃) solution is required. Because of that this method is expensive and extensive. Furthermore accelerated aging takes place because of Na₂CO₃ particles in the coating surface, which leads to a reduction of the transmission, as described by Helsch, Journal of Non-Crystalline Solids, 265, pp. 193 to 197 (2000).

[0011] The poor adherence of porous SiO₂ coatings is also a problem for other chemically resistant glasses, with alkali-poor or alkali-free glasses, for example, silica glass.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to prepare an anti-reflective coated alkali-poor or alkali-free glass body, for example quartz glass, having a coating with increased adherence and wash resistance.

[0013] This object is attained by an alkali-free or alkali-poor glass body according to the invention, preferably a borosilicate glass body, which has a porous coating at least on one of its sides, which contains phosphorous as well as SiO₂. This anti-reflective coating on this body is both adherent and wash resistant.

[0014] The alkali-poor or alkali-free glass is understood to mean a glass that contains no alkali metal oxides or less than 12 percent by weight alkali metal oxides in the context of the present invention.

[0015] The rubbing test according to DIN 58196-5 provides a measure of the adherence and wash resistance of the coating. A coating on a body that fulfills the test criterion of 2 or better (no rubbed off material, only rubbing scratches or tracks detectable) during the testing according to this DIN procedure is very rubbing resistant and thus also very adherent and very wash resistant.

[0016] In a preferred embodiment of the invention the phosphorous provided in the coating is provided by a phosphorous oxide compound. Good results were obtained for the rubbing resistance with the phosphorous oxide compounds.

[0017] A glass body, which contains from 1 to 20 percent by weight, preferably at least 3 percent by weight, and especially preferably at least 7 percent by weight, of a boron oxide ingredient, is especially preferred.

[0018] In a particularly preferred embodiment of the invention the glass body according to the invention has a composition (in percent by weight on an oxide basis) of from 70 to 85 percent by weight, SiO₂; from 7 to 15 percent by weight, B₂O₃; from 2 to less than 12 percent by weight, preferably from 2 to less than 10 percent by weight, Na₂O+K₂O; from 1 to 8, preferably from 1 to 7, percent by weight, Al₂O₃; from 0 to 11, percent by weight RO, wherein RO represents one or more ingredient from the group consisting of MgO, CaO, SrO, BaO and ZnO.

[0019] A glass body, which has an alkali oxide content of from 0 to less than 5 percent by weight, preferably from 0 to 1 percent by weight, is also a preferred embodiment of the invention.

[0020] In an especially preferred embodiment the glass body according to the invention the glass body contains (in percent by weight on an oxide basis) of from 40 to 60 percent by weight, SiO₂; from 7 to 15 percent by weight, B₂O₃; from 8 to 20 percent by weight, Al₂O₃; from 0 to 30 percent by weight RO, wherein RO represents one or more ingredient from the group consisting of MgO, CaO, SrO, BaO and ZnO.

[0021] A preferred embodiment of the glass body according to the invention has a silicon oxide content of at least 95% by weight is. An especially preferred embodiment of the glass body contains at least 99 percent by weight silicon oxide. A most preferred embodiment comprises quartz glass.

[0022] A preferred embodiment of the invention is a coated glass body having a coating with a pore diameter of 2 nm to 50 nm. In this pore size range good reflection reduction is obtained.

[0023] Another preferred embodiment of the invention comprises a coated glass body, in which the porosity amounts to 10 percent to 60 percent of the total volume of the coating. In this range for the porosity good reflection reduction ise obtained.

[0024] A coated glass body in which the weight ratio of SiO₂ to P₂ O₅ in the coating amounts to 10:1 to 1:1 is especially preferred. Especially good rubbing resistance is attained with these ratios of SiO₂ to P₂O₅.

[0025] A coated glass body in which the weight ratio of SiO₂ to P₂O₅ in the coating amounts to 3:1 to 1.2:1 is even better. Particularly good rubbing resistance is attained with these ratios of SiO₂ to P₂O₅.

[0026] An additional preferred embodiment of the invention comprises a coating glass body having a coating thickness of 50 nm to 500 nm. Good reflection reduction is obtained when the coating thickness is in this range.

[0027] In an especially preferred embodiment of the invention the coated glass body has a coating thickness of from 80 nm to 160 nm. Good reflection reduction is obtained when the coating thickness is in this range.

[0028] The porous coating on the glass body according to the invention for example can be produced by application of a solution. The solution can, for example, be applied by spraying, casting or dipping.

[0029] A method of making the glass body according to the invention includes

[0030] a) dipping the glass body in a volatile solution containing H₃PO₄ and SiO₂,

[0031] b) withdrawing the glassbody from the solution; and

[0032] c) tempering the glass body at a temperature under T_(g) of the glass.

[0033] Coated glass is made by the method according to the invention having coatings that have a high adherence, a high wash fastness and a high reflection reduction. With the method according to the invention the coating can preferably be made rubbing resistant in a single step. After dipping or immersing the glass body must no longer be dipped in a NaHCO₃ solution, which up to now in the known method was required to make a porous coating on borosilicate glass. That means that the method has a great commercial advantage. The method is performed faster, since less processing time is required. The required number of plant components is reduced. Raw material need is reduced. Waste disposal of spent NaHCO₃ solution is no longer needed.

[0034] The above-described method is outstandingly suitable for alkali-free or alkali poor glasses.

[0035] The glass body can be pre-cleaned in one or more cleaning steps prior to the dipping or immersing. For example, water, lower chain alcohols or ketones can be used as the cleaning agent in the pre-cleaning.

[0036] According to a preferred embodiment the glass body is withdrawn from the solution in method step b) at a speed of 0.1 mm/s to 100 mm/s, preferably from 1 mm/s to 20 mm/s. Higher drawing speeds are possible by lowering the viscosity. The lower viscosity of the solution is achieved, for example, by reducing the content of SiO₂ and H₃PO₄ and by changing the solvent.

[0037] According to the invention the solution, which is suitable for use in the above-described manufacturing methods and for coating the various alkali-free to alkali-poor glass bodies, contains an SiO₂ sol and H₃PO₄ and one or more additional acids, which adjust the pH to 1 or 2, as well as a solvent. The solution preferably contains HCl or HNO₃ as the acid ingredient. The solution contains one or more lower chain alcohols.

[0038] A preferred embodiment of the solution according to the invention for making the porous SiO₂- and phosphorous-containing coating contains from 0.1 to 2 percent by weight HCl or from 0.1 to 2 percent by weight HNO₃, from 0.1 to 6 percent by weight H₃PO₄, from 0.5 to 15 percent by weight SiO₂ sol and at least one lower chain alcohol. With this solution porous layers are obtained, which are especially rubbing resistant and provide a glass body with increased transmittance.

[0039] An especially preferred embodiment of the solution according to the invention for making the porous SiO₂- and phosphorous-containing coating contains from 0.1 to 2 percent by weight HCl or from 0.1 to 2 percent by weight HNO₃, from 0.1 to 3.5 percent by weight H₃PO₄, from 0.5 to 7 percent by weight SiO₂ sol and at least one lower chain alcohol. With this solution porous layers are obtained, which are especially rubbing resistant and provide a glass body with increased transmittance.

[0040] According to an entirely preferred form of the invention the lower chain alcohol or alcohols acting as the solvent in the solution for making the porous SiO₂- and phosphorous-containing coating have a general formula C_(n)H_(2n+1)OH with n=1, 2, 3, 4 or 5. Porous coatings are obtained with this solution, which are especially completely rubbing resistant and provide a glass body with increased transmittance.

[0041] The glass bodies according to the invention, preferably made of borosilicate glass, in the form of glass tubing, glass rod or glass panes, are used for making solar energy apparatuses. The coated glasses according to the invention are especially suitable for use in the field of solar energy, especially in waster water heating, process heat production and in parabolic channel power plant engineering.

[0042] The invention is now explained in further detail by examples.

EXAMPLES

[0043] Preparation of the Solution

[0044] A solution was prepared from 10 g isopropanol and 0.5 g 1M HNO₃ and stirred from 12 min. Then 0.8 g of 85% H₃PO₄ were added and after that stirred for 5 min. After that 1.9 grams of silica sol R40 were added (Bad Köstritz Chemical Works, SiO₂ content, 40%) and stirred for 5 min. Then the solution was allowed to stand for one day. The pH value of the solution was from 1 to 2.

[0045] Coating Method

[0046] A glass tube (DURAN®, Schott Glass Tubing, composition, in weight percent on an oxide basis: 80%, SiO₂; 13%, B₂O₃; 2.5%, Al₂O₃; 3.5%, Na₂O; 1%, K₂O) with an outer diameter of 100 mm and a wall thickness of 2.5 mm was completely immersed in the solution, left in the solution for 10 sec and subsequently withdrawn from it with a speed of 1 mm/s. Then it was tempered from 1 hour at 500° C.

Comparative Example

[0047] The glass tube of the same type and dimensions was coated with exactly the same coating method, but with a comparative solution, as in the case of the above example of the invention. The comparative solution was exactly the same as the above solution used in the coating method of the invention, except that it did not contain any phosphorous. The coating thus contained no phosphorous.

[0048] Rubbing Test

[0049] The rubbing strength or resistance was tested according to DIN 58196-5 in the case of the example. The results for the example of the invention showed that the example of the coatings of the invention fulfilled criterion 2 with an intensity of testing H50, since no coating material was eroded or rubbed off.

[0050] The rubbing resistance for the comparative example was also tested. The comparative coating fulfilled criterion 5, since the coating was worn away or worn off down to the substrate, even with an intensity of testing that was less than with the example of the invention, namely H25.

[0051] For the example according to the invention a tape test according to DIN 58196-6 was also performed. No coating material was lost with an intensity of testing K2.

[0052] The comparison of the coating of the example, which was made with the solution to which H₃PO₄ was added, with the comparative example, in which the solution contained no phosphorous, shows that the coatings made by the method according to the invention have surprisingly and unexpectedly more rubbing resistance as well as better adherence and wash resistance.

[0053] Thus for the first time alkali-poor and even alkali-free glasses can be coated with porous SiO₂-containing coatings, which fulfill the criterion 2 or better during a rubbing resistance test according to DIN 58196-5, intensity of testing H50 and experience no coating material losses during a tape test according to DIN 58196-5, intensity of testing K2. The coatings of the invention are also wash resistant, adherent and have good anti-reflection properties.

[0054] These coatings fit the requirements of the above-named application, especially the requirements that they are used for building in the glass bodies, for example into holders, roof structures and the like.

[0055] The disclosure in German Patent Application 102 09 949.9-45 of Mar. 6, 2002 is incorporated here by reference. This German Patent Application describes the invention described hereinabove and claimed in the claims appended hereinbelow and provides the basis for a claim of priority for the instant invention under 35 U.S.C. 119.

[0056] While the invention has been illustrated and described as embodied in a method of making a glass body with a phosphorous- and porous SiO₂-containing coating, glass body made thereby and solution for making same, it is not intended to be limited to the details shown, since various modifications and changes may be made without departing in any way from the spirit of the present invention.

[0057] Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

[0058] What is claimed is new and is set forth in the following appended claims. 

We claim:
 1. An alkali-free or alkali-poor glass body having a plurality of sides and provided with an adherent and anti-reflective coating on at least one of said sides, wherein said coating contains phosphorous and porous SiO₂.
 2. The glass body as defined in claim 1, wherein said adherent and anti-reflective coating has a rubbing resistance criterion according to DIN 58196-5, intensity of testing H50, of 2 or better.
 3. The glass body as defined in claim 1, containing at least 1 percent by weight boron oxide.
 4. The glass body as defined in claim 3, containing at least 7 percent by weight of said boron oxide.
 5. The glass body as defined in claim 3, containing at most 20 percent by weight of said boron oxide.
 6. The glass body as defined in claim 1, containing the following ingredients, in percent by weight on the basis of oxides: SiO₂ 70 to 85, B₂O₃  7 to 15, Na₂O + K₂O  2 to ’112, Al₂O₃  1 to 8, HO O to 11;

wherein RO represents at least one member selected from the group consisting of MgO, CaO, SrO, BaO and ZnO.
 7. The glass body as defined in claim 1, containing the following ingredients, in percent by weight on the basis of oxides: SiO₂ 40 to 60,  B₂O₃ 7 to 15, Al₂O₃ 8 to 20, RO 0 to 30;

wherein RO represents at least one member selected from the group consisting of MgO, CaO, SrO, BaO and ZnO.
 8. The glass body as defined in claim 1, containing at least 95 percent by weight of said SiO₂.
 9. The glass body as defined in claim 8, containing at least 99 percent by weight of said SiO₂.
 10. The glass body as defined in claim 1, wherein said phosphorous is present in said coating as phosphorous oxide.
 11. The glass body as defined in claim 10, wherein said phosphorous oxide is P₂O₅ and a weight ratio of said SiO₂ to said P₂O₅ in said coating is from 10:1 to 1:1.
 12. The glass body as defined in claim 11, wherein said weight ratio is from 3:1 to 1.2:1.
 13. The glass body as defined in claim 1, further comprising from 0 to 1 percent by weight of at least one alkali metal oxide.
 14. The glass body as defined in claim 13, containing the following ingredients, in percent by weight on the basis of oxides: SiO₂ 40 to 60,  B₂O₃ 7 to 15, Al₂O₃ 8 to 20, RO 0 to 30;

wherein RO represents at least one member selected from the group consisting of MgO, CaO, SrO, BaO and ZnO.
 15. The glass body as defined in claim 13, containing at least 95 percent by weight of said SiO₂.
 16. The glass body as defined in claim 15, containing at least 99 percent by weight of said SiO₂.
 17. The glass body as defined in claim 13, wherein said phosphorous is present in said coating as phosphorous oxide.
 18. The glass body as defined in claim 17, wherein said phosphorous oxide is P₂O₅ and a weight ratio of said SiO₂ to said P₂O₅ in said coating is from 10:1 to 1:1.
 19. The glass body as defined in claim 18, wherein said weight ratio is from 3:1 to 1.2:1.
 20. The glass body as defined in claim 1, wherein said coating has a coating thickness of 50 nm to 500 nm.
 21. The glass body as defined in claim 20, wherein said coating thickness is 80 nm to 160 nm.
 22. The glass body as defined in claim 1, wherein said coating is provided with pores with a pore diameter of 2 nm to 50 nm.
 23. The glass body as defined in claim 1, wherein said coating has a porosity of 10 to 60 percent by volume based on a total volume of said coating.
 24. A method of making an alkali-free or alkali-poor glass body having a plurality of sides and provided with an adherent and anti-reflective coating on at least one of said sides, wherein said coating contains phosphorous and porous SiO₂, said method comprising the steps of: a) dipping the glass body in a volatile solution containing H₃PO₄ and SiO₂, b) withdrawing the glass body from the solution; and c) tempering the glass body at a temperature under T_(g) of the glass.
 25. The method as defined in claim 24, whereby said adherent and anti-reflective coating has a rubbing resistance criterion according to DIN 58196-5, intensity of testing H50, of 2 or better.
 26. The method as defined in claim 24, wherein said withdrawing of said glass body from said solution takes plate at a withdrawing speed of from 0.1 mm/s to 100 mm/s.
 27. The method as defined in claim 26, wherein said withdrawing speed is from 1 mm/s to 20 mm/s.
 28. The method as defined in claim 24, wherein said solution has a pH of from 1 to 2 and contains at least one acid, an SiO₂ sol and at least one solvent.
 29. The method as defined in claim 28, wherein said at least one solvent is at least one lower chain alcohol having a formula C_(n)H_(2n+1)OH, with n=1, 2, 3, 4 or 5 and said at least one acid is selected from the group consisting of HCl and HNO₃.
 30. A solution for making a porous silica and phosphorous-containing coating on a glass body, wherein said solution has a pH of from 1 to 2 and contains H₃PO₄, at least one acid, an SiO₂ sol and at least one solvent.
 31. The solution as defined in claim 30, wherein said at least one solvent is at least one lower chain alcohol having a formula C_(n)H_(2n+1)OH, with n=1, 2, 3, 4 or 5 and said at least one acid is selected from the group consisting of HCl and HNO₃.
 32. The solution as defined in claim 31, containing from 0.1 to 2 percent by weight of said HCl or from 0.1 to 2 percent by weight of said HNO₃, from 0.5 to 15 percent by weight of said SiO₂ sol and from 0.1 to 6 percent by weight of said H₃PO₄.
 33. The solution as defined in claim 31, containing from 0.1 to 2 percent by weight of said HCl or from 0.1 to 2 percent by weight of said HNO₃, from 0.5 to 7 percent by weight of said SiO₂ sol and from 0.1 to 3.5 percent by weight of said H₃PO₄.
 34. A solar energy apparatus comprising a glass tube, glass rod or a glass pane, wherein said glass tube, said glass rod or said glass pane is provided with an adherent and anti-reflective coating on at least one side thereof, and wherein said coating contains phosphorous and porous SiO₂ and has a rubbing resistance criterion according to DIN 58196-5, intensity of testing H50, of 2 or better. 